Prescription eyeglass lenses are curved in such a way that light is correctly focused onto the retina of a patient's eye, improving vision. Such lenses are formed from glass or plastic lens “blanks” having certain desired properties to provide the correct prescription for the patient. The blanks are usually circular and of substantially larger dimension, for example 70 mm in diameter and 10 mm, compared to the relatively smaller finished lenses assembled into eyeglass frames. Therefore, a lens blank must be edged to fit an eyeglass frame selected by the patient.
Ophthalmic laboratory technicians cut, grind, edge, and polish blanks according to prescriptions provided by dispensing opticians, optometrists, or ophthalmologists. In addition, the large diameter blank is sized and shaped to fit into the frame selected by the patient. The lens blank may be shaped using an edger, such as the lens edger disclosed in U.S. Pat. No. 6,203,409 to Kennedy et al., the disclosure of which is incorporated herein by reference. The blank is edged so that the periphery of the finished lenses fit into the openings on the frames.
Edging of a lens blank typically requires the application of a block to a surface thereof. The block is releasably secured to a clamp assembly, so that rotation of the clamp assembly causes corresponding rotation of the lens blank. As the blank is rotated, the periphery of the blank may be cut to a desired size using a router tool. The lens periphery may also be polished using a polishing tool. A bevel is often formed about the lens, particularly adjacent the wearer.
The finished lens may then be assembled with the selected eyeglass frames. The frames include two spaced openings in which the finished lenses are mounted. The frame openings frequently have a bevel or a tongue, which interlocks with a complementarily shaped bevel or groove, respectively, formed about the peripheral edge of the lens. The interlock between the complementary bevel and groove helps to secure the lens within the opening. The router and polishing tools on the edger form the bevel or groove about the lens.
The configuration of the bevel or groove that is edged into the peripheral edge of the lens may vary depending on the configuration of the bevel or tongue in the frame openings. Therefore, various router and polishing tools are provided for forming different bevel or groove configurations. In addition, some frame designs are secured to protrusions extending from the peripheral edge of the lens. Such protrusions are often difficult to form using router blades having a relatively large diameter. Instead, the protrusions may be formed using an end mill cutter.
The router tools, polishing tools and end mill cutters are interchangeably secured on the edger via a shaft and chuck assembly. Thus, the technician must change the tool each time a different configuration of the lens edge is needed.